/Engine/Plugins/FX/Niagara/Source/Niagara/Public/NiagaraPreviewGrid.h
Base class for all preview axis types. NiagaraPreviewGrid uses these to control how many systems to spawn in each axis and how each system varies on that axis. C++ Examples are show below. You can also create these as Blueprint classes as show in the Plugin content folder.
[UCLASS](Programming/UnrealArchitecture/Reference/Classes#classdeclaration)(Abstract, EditInlineNew, BlueprintType, Blueprintable) class UNiagaraPreviewAxis : public [UObject](API\Runtime\CoreUObject\UObject\UObject)